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tfje  Specific  (irabttteg  of 
anb  tantalum 


MAURICE  ALLISON  LAMME 


On  the  Specific  Gravities 


OF 


Niobium  and  Tantalum  Pentoxides 


BY 
MAURICE  ALLISON  LAMME,  B.S..  A.M. 


DISSERTATION 

SUBMITTED   IN   PARTIAL    FULFILLMENT   OF   THE    REQUIREMENTS    FOR    THE 

DEGREE  OF  DOCTOR  OF  PHILOSOPHY  IN  THE  FACULTY  OF 

PURE  SCIENCE  OF  COLUMBIA  UNIVERSITY 


LANCASTER,  PA. 

STEINMAN  &  FOLTZ, 

1909 


? 

0 


ACKNOWLEDGMENT 

This  investigation  was  undertaken  at  the  suggestion  of  and 
carried  out  under  the  direction  of  Dr.  Floyd  J.  Metzger,  to  whom 
I  here  wish  to  express  my  appreciation. 

M.  A.  L. 

QUANTITATIVE  CHEMICAL  LABORATORY, 

HAVEMEYER  HALL,  COLUMBIA  UNIVERSITY, 

MARCH  1,  1909. 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 


PURPOSE 

THE  original  purpose  of  this  investigation  was  to  find  a  method 
for  the  determination  of  tantalum  and  niobium,  without  separa- 
tion, based  on  the  specific  gravity  of  the  combined  oxides.  Until 
recently,1  the  only  available  method  for  their  determination  was 
by  fractional  crystallization  of  the  potassium  double  fluorides. 
In  this  method  the  mixed  hydroxides  of  the  elements  are  obtained 
by  fusion  with  potassium  bisulphate  and  boiling  the  melt  with 
water.  After  removal  of  impurities  and  thorough  washing,  these 
hydroxides  are  dissolved  in  hydrofluoric  acid,  potassium  fluoride 
added  and  the  solution  evaporated  until  the  more  insoluble  tan- 
talum salt  separates.  It  is  a  difficult  matter  to  free  this  salt 
from  the  mother  liquor  containing  the  niobium  without,  at  the 
same  time,  dissolving  some  of  the  tantalum  salt.  That  the 
method  is  inaccurate  and  unreliable,  is  shown  by  Metzger  and 
Taylor.2 

Penfield  and  Ford,3  in  an  article  on  Stibiotantalite,  in  which 
tantalum  and  niobium  were  determined  by  a  method  based  on 
the  specific  gravity  of  the  combined  oxides,  say  "As  there  is  no 
satisfactory  method  for  separating  tantalum  from  niobium,  the 
attempt  has  been  made  to  determine  the  proportions  of  the  two 
oxides  by  taking  the  specific  gravity  of  the  mixed  oxides  as  ob- 
tained from  the  analysis,  and  comparing  the  results  with  those 
of  pure  Ta2O5  and  Nb205,  which  are  quite  widely  separated. 
This  method  has  been  tested  sufficiently  to  prove  that  it  gives 
fairly  satisfactory  results.  .  .  .  The  greatest  variation  of  the 
determination  of  Nb20s  from  these  curves  is  not  over  one  per 
cent.,  which  is  well  within  the  errors  of  analysis." 

It  was  thought  that  if  the  specific  gravities  of  the  oxides  were 


*"A  New  Rapid  Volumetric  Method  for  the  Determination  of  Niobium  in 
the  Presence  of  Tantalum,"  Metzger  and  Taylor,  to  be  published  soon. 
2Loc.  Cit. 
3"Am.  Jour.  Science,"  1906,  p.  72. 


211037 


4        Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

accurately  determined  under  conditions  which  gave  constant 
results,  9  curve  could  be  used  which  would  give  the  percentage 
of  each  oxide  in  a  mixture  by  its  specific  gravity.  This  would 
obviate  the  separation  of  the  elements  in  the  analysis  and  greatly 
shorten  it.  In  order  to  do  this  and  have  the  results  accurate  to 
within  0.25  per  cent.,  it  was  found  that  the  specific  gravity  must 
be  accurate  to  the  third  decimal.  This  meant  even  greater 
accuracy  in  the  weights  of  the  specific  gravity  flask  and  the  liquid 
used.  It  was  necessary  that  these  weights  should  check  within 
0.0005  gm.  This  was  one  of  the  most  difficult  problems.  The 
weights  did  not,  as  a  rule,  check  within  this  limit,  notwithstand- 
ing the  fact  that  various  forms  of  apparatus  were  employed. 

While  the  work,  primarily,  had  this  object  in  view,  it  was 
found  necessary  later  to  change  the  purpose  somewhat,  and, 
therefore,  the  investigation  has  been  divided  into  three  parts. 

PREPARATION  AND  PROPERTIES  OF  THE  MATERIAL 

The  niobium  and  tantalum  oxides  employed  in  this  work  were 
prepared  from  South  Dakota  columbite  by  fusion  with  potassium 
bisulphate,  boiling  with  water,  removing  impurities  as  usual, 
leaving  the  mixed  hydroxides  of  niobium  and  tantalum,  which 
were  then  converted  to  oxides  and  separated  as  follows:  The 
mixed  oxides  were  treated  in  small  portions  by  fusion  with  crys- 
tallized potassium  bisulphate  (the  crystallized  bisulphate  is  much 
more  effective  in  decomposing  the  mixed  oxides  than  is  the  fused 
pyrosulphate),  sulphuric  acid  added  to  the  melt  to  make  it 
pasty,  the  mass  poured  into  hot  water,  boiled  and  washed  several 
times  with  hot  water  by  decantation,  the  hydroxides  transferred 
to  a  filter  (using  a  hard  rubber  funnel)  and  the  washing  with 
boiling  water  continued  until  thoroughly  washed.  The  hydrox- 
ides so  obtained  were  dissolved  through  the  filter  paper  with 
hydrofluoric  acid.  When  about  a  liter  of  this  hydrofluoric  acid 
solution  had  been  obtained,  somewhat  more  than  the  required 
amount  of  potassium  fluoride  to  form  the  double  salt  was  added 
and  the  solution  evaporated  in  a  large  silver  dish  until  crystals 
of  the  tantalum  double  fluoride,  K2TaF7,  began  to  form  on  the 
surface.  These  crystals  are  long,  fine  needles.  However,  if  the 
solution  contains  too  much  hydrofluoric  acid,  a  niobium  salt 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides        5 

separates  in  short  prisms,  not  unlike  the  tantalum  salt,  but  larger, 
and  more  insoluble  than  potassium  niobium  oxyfluoride, 
K2NbOFs.H20.  The  amount  of  acid  present  should  be  only 
sufficient  to  keep  the  tantalum  salt  in  solution,  i.  e.,  about  1 
to  2  cc.  per  100  cc.  of  solution. 

As  soon  as  crystals  of  tantalum  began  to  form,  the  solution  was 
allowed  to  cool  slowly,  the  crystals  filtered  off,  washed  two  or 
three  times  with  cold  water  and  allowed  to  drain.  The  solution 
was  then  further  concentrated  and  a  second  crop  of  crystals 
obtained,  which  was  kept  separate  from  the  first.  On  the  third 
concentration,  the  solution  was  tested  from  time  to  time  by 
taking  out  a  drop  or  two  of  the  liquid  and  allowing  to  cool  to  note 
the  presence  or  absence  of  the  niobium  crystals.  The  niobium 
double  fluoride  crystallizes  in  lustrous  plates  easily  distinguished 
from  the  tantalum  salt,  When  the  proper  concentration  had 
been  reached,  as  shown  by  the  above  test,  the  solution  was 
allowed  to  cool.  The  crystals  obtained  at  this  point,  being  a 
mixture  of  both  salts,  were  rejected.  The  mother  liquor  from 
these  mixed  crystals  was  concentrated  until  two  crops  of  the 
potassium  niobium  oxyfluoride  were  obtained.  These  two  frac- 
tions of  the  niobium  salt  were  kept  separate.  The  mother  liquor 
was  rejected. 

These  operations  were  repeated  until  all  the  oxides  were  con- 
verted into  the  double  fluorides  and  the  mixed  fluorides  separated. 
All  the  " first  crop"  of  tantalum  salt  was  combined  and  recrystal- 
lized  once.  To  the  mother  liquor  from  this  the  entire  "  second 
crop"  of  crystals  was  added  and  one  crystallization  made.  The 
crystals  from  the  last  mother  liquor  were  rejected.  Finally,  the 
two  crops  of  crystals  just  obtained  were  united  and  recrystal- 
lized  and  the  mother  liquor  rejected.  This  final  lot  of  crystals 
constituted  the  material  used  in  the  subsequent  work  on  tan- 
talum. For  the  K^NbOFs.H^O  the  same  general  method  of 
purification  was  employed. 

There  seems  to  be  considerable  lack  of  agreement  among 
investigators  with  regard  to  the  specific  gravities  and  properties 
of  the  oxides  of  niobium  and  tantalum,  as  may  be  seen  in  the 
following  paragraphs. 


6        Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

Abegg1  gives  the  properties  of  tantalum  pentoxide  as  a  taste- 
less and  odorless  white  powder  which  suffers  no  chemical  change 
on  heating.  By  continued  heating,  it  becomes  crystalline. 
Ebelmen2  obtained  well-formed  orthorhombic  prisms  by  heating 
Ta2(>5  in  a  muffle  furnace  with  phosphorous  salt,  which  were 
crystallographically  investigated  by  Mallard3  and  by  Norden- 
^kjoid  and  Chydenius.4 

The  specific  gravity  varies  according  to  the  method  or  prepa- 
ration and  is  especially  influenced  by  the  length  of  time  and  in- 
tensity of  heating,  as  is  shown  in  the  following  example  from 
Rose:'5 

The  specific  gravity  of  the  oxide  was  7.109. 

Heated  1  Hour  at 

Moderate  Heat.      4}  Hours.  9£  Hours.  15£  Hours. 

7.274  7.383  7.529  7.536 

And  after  a  further  heating  of  eleven  hours  at  a  high  temperature, 
7.914.  On  still  further  heating,  it  rose  to  7.994.  By  heating 
strongly  in  a  furnace,  it  sank  to  7.652,  because  the  Ta20s  became 
amorphous.  On  fusion  with  potassium  bisulphate  and  again 
heating  the  hyrdoxide,  the  specific  gravity  was  8.257. 

The  values,  given  in  the  literature,  vary  between  7.03  and  8.26.6 
It  is  to  be  remarked,  however,  that  many  of  the  old  determina- 
tions are  quite  unreliable  on  account  of  the  use  of  impure  Ta20g. 

In  all  cases  in  which  the  decomposition  of  the  tantalum  com- 
pounds has  been  effected  by  the  use  of  potassium  bisulphate,  the 
product  contains  sulphuric  acid,  which  cannot  be  removed  by 
washing.  To  get  rid  of  this,  the  hydroxide  must  be  heated  with 
ammonium  carbonate. 

Niobium  pentoxide  can  be  obtained  by  heating  E^NbOFs.H^O 
with  sulphuric  acid  in  a  platinum  crucible  until  all  the  hydro- 


1"Handbuch  der  Anorganischen  Chemie,"  Vol.  Ill,  part  III,  p.  853. 
2  "Ann.  Chim.  Phys."  (3),  33,  34. 
3Compt.  Rend.,  105,  1260. 

4"Oefvers  af.  k.  Vet.  Ak.  Forh,"  1860,  3;  "Pogg.  Ann.,"  110,  642. 
5"Pogg.  Ann.,"  74,  285. 

6 Rose,  "Marignac,  Ann.  Chim.  Phys."    (4),  9,  249;  Deville  and  Troost, 
"Compt.  Rend.."  60,  1121. 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides        7 

fluoric  acid  is  driven  off,  boiling  the  residue  with  water,  washing 
and  heating.  The  precipitate  must  be  washed  with  ammonia 
before  it  is  heated,  to  remove  the  sulphuric  acid.  Obtained  in 
this  manner,  it  usually  contains  traces  of  alkali. 

The  specific  gravity  of  the  oxide  varies  between  4.37  and  4.46 
when  prepared  by  means  of  potassium  bisulphate,  and  between 
4.51  and  4.53  when  prepared  by  heating  ammonium  niobium 
oxyfluoride.1  Strongly  heated,  the  oxide  becomes  crystalline. 

APPARATUS  EMPLOYED 

A  pycnometer  of  about  30  cc.  capacity,  with  a  thermometer 
ground  in,  was  first  tried,  but  it  was  found  that  the  evaporation 
of  the  water  from  the  ground  glass  joint  gave  such  variable  re- 
sults that  this  form  could  not  be  used.  Then,  a  specific  gravity 
flask  with  a  long  neck,  fine  ground,  20  cc.  capacity  and  provided 
with  a  cap  ground  in  the  same  manner,  was  used.  The  bottle 
itself,  but  not  the  neck,  was  surrounded  with  a  vaccuum  jacket. 
This  was  to  guard  against  changes  in  temperature  in  handling, 
etc.  The  object  in  having  such  a  long  neck  was  to  insure  a  good, 
tight  joint,  so  there  would  be  the  least  possible  difference  in  the 
volumes  of  the  liquid  in  the  flask  in  separate  determinations, 
caused  by  slight  differences  in  pressure  exerted  in  inserting  the 
stopper.  The  cap,  ground  in  the  same  way,  fitted  over  the 
stopper,  was  to  prevent  any  evaporation  from  the  surfaces, 
between  the  neck  and  the  stopper  or  from  the  top  of  the  capillary 
tube  in  the  stopper.  This  combination  was  found  somewhat 
too  heavy  and  cumbersome,  and  a  similar  flask,  having  a  capacity 
of  10  cc.,  was  substituted  later.  This  was  used  in  most  of  the  work 
with  water,  but  when  chloroform  was  used,  the  flask  was  essen- 
tially like  that  above,  except  that  there  was  no  vacuum  jacket. 

It  was  found  extremely  difficult  to  obtain  weights  that  checked 
within  the  desired  limits.  The  total  variation  in  the  weights  is 
great,  but  those  taken  within  short  periods  of  time  checked 
much  better. 

METHOD 

The  method  used  in  the  first  part  of  the  work  is  essentially  as 


iMarignac,  "Ann.  de  Chim.  et  Phys."  (4),  8,  19. 


8        Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

given  below.  Some  changes  were  made  from  time  to  time  to 
suit  new  conditions. 

The  flask  was  weighed  filled  with  water,  the  water  poured  out 
and  a  weighed  amount  of  oxide  in  fine  powder  introduced,  the 
air  removed  as  explained  later,  the  flask  filled  and  weighed  again. 
The  difference  in  weight  between  the  flask  with  the  oxide  and 
with  water  only  was  subtracted  from  the  amount  of  oxide,  and 
the  amount  taken  divided  by  this  value,  giving  the  specific 
gravity. 

In  preparing  the  flask  for  weighing,  the  stopper  was  inserted 
each  time  with  as  near  as  possible  the  same  pressure.  Then  all 
superfluous  moisture  was  removed,  that  from  the  top  of  the 
capillary  tube  removed  last,  and  the  cap  put  on.  It  was  found 
that  much  better  weights  could  be  made  if  the  flask  were  now 
dipped  in  cold  water  and  carefully  dried  with  a  clean  cloth.  After 
standing  ten  minutes  in  the  balance  case,  the  weight  was  taken. 
The  oxide  must  be  in  a  fine  powder  to  reduce  to  a  minimum  the 
possibility  of  included  air.  As  a  further  precaution,  after  in- 
troducing the  oxide  the  flask  was  only  partially  filled  with  water, 
shaken  with  a  rotary  motion  and  the  filling  completed.  In 
completing  the  filling  it  was  necessary  to  run  the  water  in  slowly 
in  order  to  leave  a  clear  portion  above  that  which  had  been 
shaken  up,  otherwise  some  of  the  fine  oxide  held  in  suspension 
would  be  lost  when  the  stopper  was  inserted. 

The  oxides  were  prepared  from  the  double  fluorides  as  follows: 
A  portion  of  the  double  fluoride,  corresponding  roughly  to  1.00 
gram  of  the  oxide,  was  heated  in  a  platinum  dish  with  sulphuric 
acid  until  all  the  hydrofluoric  acid  had  been  driven  off  and  copious 
fumes  of  SOs  evolved.  After  cooling,  the  solution  was  slowly, 
and  with  vigorous  stirring,  poured  into  about  700  cc.  of  hot  water. 
This  was  then  boiled,  the  water  poured  off  through  a  filter  after 
allowing  the  hydroxide  to  settle,  boiled  up  with  about  the  same 
quantity  of  water  twice  more,  and  then  filtered.  The  hydroxide, 
while  still  moist,  was  placed  in  a  large  platinum  crucible  and 
gently  heated  until  dry.  After  this,  the  heat  was  raised,  the 
paper  burned  off  and  the  resulting  oxide  pulverized  in  an  agate 
mortar  to  approximately  80  mesh. 

On  trying  to  filter  the  oxides  after  a  determination,   it  was 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides        9 

found  that  nearly  all  of  the  finer  portions  ran  through  the  paper. 
This  solution,  if  left  undisturbed,  would  remain  cloudy  for  several 
weeks.  On  account  of  the  difficulty  of  filtering,  not  more  than 
one  value  was  obtained  from  each  portion  in  the  first  part  of  the 
work.  It  is  possible  that  some  of  this  finer  portion  was  rehy- 
drated  to  some  extent  (?). 


10       Specific  Gravities  of  Niobium  and  Tantalum  Pentoxdies 


EXPERIMENTAL 

PART  I 

In  this  part  of  the  work  the  flask  was  filled  with  boiled  dis- 
tilled water  at  room  temperature,  temperatures  being  recorded 
by  a  thermometer,  graduated  to  read  to  0.2°  C.,  and  the  usual 
precautions  taken  in  weighing.  It  was  found  that  the  weight 
of  the  flask  filled  with  water  must  be  taken  before  each  determin- 
ation, since  the  variation  in  the  temperature  of  the  water  from 
day  to  day  caused  such  a  variation  in  the  weight  that  a  constant 
value  could  not  be  used.  In  many  cases  the  weights  obtained 
on  one  day  did  not  check  with  those  obtained  on  the  next,  though 
the  temperature  was  the  same.  The  flask  was  handled  as  little 
as  possible  after  taking  the  temperature  in  order  to  avoid  any 
change. 

A  number  of  weighings  was  made  to  determine  the  error  in 
filling  and  in  inserting  the  stopper  and  are  given  here: 

Temperature.  Weight. 

20.8  65.2000 

20.8  65.1992 

20.8  65.1983 

20.8  65.1980 

20.8  65.2002  ] 

20.8  65.2002  | 

20.8  65.1987  [  b 

20.8  65.1978  | 

20.8  65. 1972  J 

In  a  series  of  weighings  the  values  varied  in  this  manner,  then, 
after  a  period  of  rest,  as  allowing  to  stand  over  night,  the  weight 
returned  practically  to  the  original  value.  Series  (a)  was  obtained 
one  day  and  series  (b)  on  the  following  day.  The  variation  was 
sometimes  in  one  direction  and  sometimes  in  the  other. 

A  number  of  determinations  was  made  to  ascertain  if  constant 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      11 

results  could  be  obtained  by  washing  the  hydroxide  with  water 
alone.  It  was  thought  that  the  sulphuric  acid  could  be  so  far 
removed  as  not  to  cause  appreciable  error,  even  though  it  is 
practically  impossible  to  remove  all  of  it. 

The  table  with  the  results  is  given  and  the  detailed  description 
of  the  conditions  of  each  experiment  follows: 

Weight  Flask     Weight  Flask  Weight           Tempera- 
No,             and  Water.  and  Oxide.  Oxide.  ture.  Gravity. 

1 65.1918  65.6066  0.5411  23.0  4.284 

2 65.1945  65.8617  0.8659  22.2  4.357 

3 65.2020  65.9425  0.9570  21.2  4.420 

4 65.1893  66.1641  1.2661  23.2  4.344 

5 65.2003  66.1697  1.2774  20.8  4.147 

6 65.2026  66.2168  1.3258  20.4  4.254 

7 65.1913  66.1797  1.2996  23.0  4.176 

8 65.1978  66.1852  1.2847  21.4  4.322 

9 65.1870  66.0078  1.0662  22.9  4.344 

10 65.1834  66.0211  1.0738  23.7  4.459 

11 65.1974  66.0128  1.0513  20.5  4.456 

(1)  About    1   gm.  K2NbOFs.H20   was  heated   with  sulphuric 
acid  until  fumes  of  80s  were  given  off,  and  the  solution  poured, 
with  stirring,  into  700  cc.  hot  water.     This  was  boiled  ten  min- 
utes, allowed  to  settle  and  boiled  with  fresh  portions  of  water 
for  the  same  length  of  time  twice  more.     The  hydroxide  was 
filtered  and  dried.     A  moderate  blast  was  then  applied  for  thirty 
minutes. 

(2)  The  same  method  of  preparation  was  followed  as  in  (1), 
except  that  the  blast  was  used  only  twenty  minutes. 

(3)  The  blast  was  here  applied  forty  minutes  and  the  method 
of  preparation  the  same  as  in  (1). 

(4)  About   3  grams  K2NbOF5.H2O  were  treated  with    20  cc. 
sulphuric  acid  and  the  solution  poured,  with  stirring,  into  two 
liters  of  hot  water,  boiled,  and  washed  on  the  filter  with  one 
liter  of  boiling  water.     The  hydroxide  did  not  settle  well.      It 
was  then  dried,  powdered  and  heated  for  one  hour  in  a  platinum 
crucible  at  a  full  red  heat. 

(5)  The  same  amount  of  K2NbOF5.H20  was  treated  as  in  (4). 
10  cc.  sulphuric  acid  were  used  and  the  hydroxide  washed  with 


12      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

two  liters  of  hot  water  on  the  filter,  after  being  boiled  with  one 
liter.     The  hydroxide  settled  well  and  washed  easily. 

(6)  The  same  amount  of  K2NbOF5.H2O  as  in  (4)  was  treated 
with  10  cc.  sulphuric  acid,  poured  into  two  liters  of  hot  water, 
boiled,  filtered  and  washed  with  three  liters  of  hot  water.    Dried 
and  heated  one  hour  in  a  platinum  crucible  at  a  full  red  heat. 

(7)  Three  grams  K2NbOF5.H02  were  treated  with  12  cc.  sul- 
phuric  acid,   hydrolyzed   in  three   liters   of   hot   water,   boiled, 
decanted  and  boiled  with  the  same  amount  four  times,  then  fil- 
tered and  dried.     A  moderate  blast  was  applied  to  the  oxide 
for  ten  minutes. 

(8)  Three  grams  K2NbOFs.H20  treated  in  the  same  manner 
as  (7). 

(9)  Two  and  a  half  grams  K2NbOF5.H20  treated  with  12  cc. 
sulphuric  acid,  hydrolyzed  in  two  liters  of  hot  water  and  boiled 
three  times  with  the  same  amount.     The  filter  paper  was  burned 
off  at  a  low  temperature  and  a  higher  blast  used  than  in  (7)  and 
(8)  for  ten  minutes. 

(10)  Two  and  a  half  KoNbOFs.H^O  treated  in  the  same  manner 
as  in  (9). 

(11)  Two  and  a  half  grams  of  K2NbOF5.H20  treated  in  the  same 
manner  as  in  (9). 

In  the  foregoing  experiments  the  oxide  increased  in  weight  on 
standing  on  the  balance  pan.  Notwithstanding  the  thorough 
washing  of  the  hydroxide  and  the  prolonged  and  intense  heating 
it  is  interesting  to  note  that  the  oxides,  when  ground  in  an  agate 
mortar,  were  invariably  slightly  sticky  and  adhered  to  the  mortar, 
due,  undoubtedly,  to  the  attraction  of  moisture  by  a  small 
amount  of  sulphuric  acid  still  present  in  the  oxide,  which  opinion 
seems  to  be  further  borne  out  in  the  subsequent  experiments. 

Another  series  was  made,  using  ammonium  hydroxide  to  neu- 
tralize the  sulphuric  acid  present. 

No.                    Weight  Oxide.  Temperature.  Gravity. 

12 1.0520                        20.5  4.974 

13 1.0772                        20.6  4.936 

14 1.0619                        22.2  5.047 

15 1.0635                        21.5  4.914 

16  ..                      .   1.0620                        22.0  4.482 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      13 

(12)  Two  and  a  half  grams  K2NbOF5.H2O  were  treated  with 
12  cc.  sulphuric  acid,  poured  into  one  liter  of  hot  water,  boiled 
and  allowed  to  settle.     Boiled  twice  more  with  one  liter  of  water, 
the  last  portion  being  made  slightly  alkaline  with  ammonium 
hydroxide  before  filtering.     The  oxide  was  heated  with  a  Chad- 
dock  burner  until  the  paper  was  burned  off,  usually  about  forty- 
five  minutes.     The  crucible  was  surrounded  with  a  clay  cylinder 
and  the  temperature  regulated  so  that  the  bottom  of  the  crucible 
was  red. 

(13)  Same  as  (12). 

(14)  Two  and  a  half  grams  K2NbOF5.H20  treated  with  12  cc. 
sulphuric  acid,  poured  into  one  liter  of  hot  water  and  washed 
twice  by  decantation  with  the  same  amount  of  hot  water,  boiling 
each  time.     No  ammonium  hydroxide  was  used  in  the  last  wash 
water.     The  same  low  heat  was  applied   until  the  paper  was 
incinerated,   the  oxide  ground   and   placed   in  a  crucible  with 
concentrated  ammonium  hydroxide  and  heated  again  for  twenty 
minutes  at  a  low  red  heat. 

(15)  Same  as  (14)  except  that  the  partially  dried  hydroxide 
was  mixed  with  ammonium  carbonate  and  heated  in  the  usual 
manner. 

(16)  Same   as   (7)    except   that   after  filtering  the   hydroxide 
was  washed  on  the  filter  with  strong  ammonia  and  on  account 
of    the  gelatinous  character,  the  precipitate   probably  did    not 
receive  a  thorough  treatment  with  the  alkali. 

In  these  experiments  the  oxide  did  not  gain  in  weight,  except 
that  of  (16),  which  apparently  still  contained  some  sulphuric 
acid.  In  the  following  work  the  last  portion  of  water  used  in 
washing  the  hydroxide  was  always  made  distinctly  alkaline  before 
filtering. 

In  the  following  determinations  about  2.5  grams  K2NbOFs.H20 
were  treated  with  12  cc.  sulphuric  acid,  poured  into  one  liter  of 
hot  water,  boiled,  washed  twice  by  boiling  and  decantation,  the 
last  wash  water  made  alkaline  with  ammonium  hydroxide.  The 
hydroxide,  after  drying  at  a  low  temperature,  was  heated  for 
one  hour  at  a  low  red  heat. 


14      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

No.                    Weight-  Oxide.             Temperature.  Gravity. 

17 1.0870  22.7  4.954 

18 1.0221  20.6  4.973 

19 1.0163  21.6  4.936 

20 1.1354  23.3  4.932 

21 1.1461  23.5  4.950 

22 1.1051  25.3  4.962 

23 1.1097  24.55  4.960 

24 1.1133  24.8  4.952 

The  average  of  these  determinations  is  4.949,  which  repre- 
sents the  value  of  the  specific  gravity  of  Nb20s  under  these  con- 
ditions. 

For  the  corresponding  value  of  the  tantalum  oxide  the  same 
conditions  were  used  in  the  preparation  of  the  oxide,  ignition, 
etc.,  as  in  the  case  of  the  niobium  oxide. 

No.                    Weight  Oxide.  Temperature.  Gravity. 

25 ...1.1745  .22.9  7.909 

26 1.1883  23.3  7.909 

27 1.1600  23.4  7.854 

28 1.2207  22.9  7.916 

29 1.1910  23.7  7.856 

30 1.2060  23.6  7.805 

31 1.1543  22.7  7.857 

These  results  give  an  average  of  7.872  as  the  specific  gravity 
of  Ta20s  under  these  conditions.  On  account  of  the  smaller 
displacement,  the  variation  is  greater  in  these  determinations 
than  that  in  the  case  of  niobium. 

Knowing  that  difference  in  the  length  of  time  and  intensity 
of  the  heat  applied  makes  a  difference  in  the  specific  gravity,  it 
was  decided  to  make  a  series  of  determinations,  using  a  higher 
temperature  for  the  same  length  of  time  as  above.  The  prepa- 
ration of  the  sample  was  the  same  as  before,  but  the  oxide  was 
heated  with  the  full  flame  of  the  Chaddock  burner  for  one  hour. 
This  gave  a  bright  orange  heat. 

No.                    Weight  Oxide.  .        Temperature.  Gravity. 

32 1.1573                        22.2  8.362 

33 1.1588                        21.9  8.277 

34 1.1574                        22.1  8.362 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      15 

No.                     Weight  Oxide.  Temperature.  Gravity. 

35  .............   1.1485  22.3  8.310 

36  ...........  .  .   1.1512  22.4  8.294 

37  .............   1.1592  22.5  8.303 

38  .............    1.1263  21.9  8.373 

39  .............    1.1604  22.0  8.371 

40  .............    1.1718  21.8  8.281 

41  .............  1.1754  21.9  8.353 


This  gives  an  average  of  8.328  as  the  specific  gravity  of 
at  a  higher  temperature. 

An  exactly  similar  series  was  made  on  niobium  pentoxide  to 
find  the  value  under  the  above  conditions. 

No.                    Weight  Oxide.             Temperature.  Gravity. 

42  .........  ____  1.1209  23.2  4.844 

43  .............  1.0951  23.1  4.849 

44  .............  1.0778  23.0  4.807 

45  .............  1.1094  23.8  4.802 

46  .............  1.0865  24.2  4.835 

47  .............  1.0867  23.2  4.806 

48  .............  1.1215  23.4  4.852 

These  results  give  an  average  of  4.828. 

This  would  seem  to  indicate  that  with  increasing  heat  the 
specific  gravity  of  the  tantalum  oxide  increases,  whereas  that  of 
the  niobium  oxide  decreases.  It  was  thought  possible  that 
there  might  be  slight  differences  in  the  hydrolysis  in  the  separate 
experiments  above,  which  would  affect  the  results,  therefore, 
two  larger  portions  of  about  double  the  quantity  of  salt  were 
taken  and  treated  as  usual.  After  the  hydroxides  had  been 
obtained,  each  of  these  was  divided  into  two  parts.  Each  pair 
of  hydroxides  was  ignited  separately  under  the  same  conditions, 
i.  e.,  the  first  pair  at  a  full  red  heat  for  one  and  a  half  hours,  the 
second  pair  at  the  same  temperature  for  two  and  a  half  hours. 

No.  Weight  Oxide.  Temperature.  Gravity. 

49  .............   1.1017  23.6  4.702 

Second  half  .....    1.1134  23.6  4.770 

50  .............    1.1713  22.9  4.370 

Second  half..      .1.1505  22.9  4.329 


16      Specific  Gravities  of  Niobium  and  Tantalum  Penioxides 

Each  pair  shows  no  greater  disagreement  than  obtains  where 
the  portions  were  prepared  separately.  The  length  of  time 
of  heating,  however,  has  a  marked  influence  on  the  values. 

Mixtures 

Using  the  average  values  obtained  for  tantalum  and  niobium 
at  a  full  red  heat,  8.328  and  4.828,  a  curve  was  plotted  and  mix- 
tures made  to  determine  whether  the  per  cent,  of  tantalum  and 
niobium  could  be  obtained  in  this  manner. 

The  pure  oxides,  or  mixtures  of  the  same,  are  usuall)'  very 
slightly  grayish  in  color  when  prepared  by  fusing  the  oxides 
with  potassium  bisuiphate,  hydrolyzing,  etc.,  but  those  prepared 
from  the  double  fluorides  are  white.  This  was  thought  due  to 
the  presence  of  a  slight  amount  of  platinum.  An  effort  was  made 
to  make  them  whiter  by  dissolving  the  hydroxides  in  hydrofluoric 
acid,  filtering,  taking  down  to  fumes  again  with  sulphuric  acid 
and  rehydrolyzing,  but  the  result  ^as  the  same.  The  color  is 
nearly  always  the  same,  and  if  there  is  any  error  due  to  this,  it 
would  be  constant. 

In  preparing  the  mixtures,  weighed  amounts  of  the  oxides 
were  fused  with  potassium  bisuiphate,  sulphuric  acid  added  to 
make  the  melt  more  fluid,  hydrolyzed  and  washed  by  decantation 
through  a  filter,  etc.,  as  already  described.  After  drying,  the 
hydroxides  were  heated  for  one  hour  at  the  full  temperature  of 
the  Chaddock  burner,  pulverized,  weighed  and  the  specific 
gravity  taken. 

The  mixture  had  the  following  proportions:  Nb2C>5,  0.5897  gm., 
and  Ta205,  0.6899  gm.,  corresponding  to  46.08  per  cent.  Nb20s 
and  53.92  per  cent.  Ta2O5-  The  specific  gravity  was  6.345, 
which,  according  to  the  curve,  gave  56.50  per  cent.  Ta20s,  an 
error  of  2.58  per  cent.1 

PART  II 

On  account  of  many  difficulties  encountered  when  water  was 
used  as  the  liquid  in  which  the  specific  gravity  was  taken,  some 
other  liquid  was  sought.  The  purpose  of  heating  of  the  oxides 
is  to  dehydrate  the  hydroxides,  and  on  being  immersed  in  water, 

!The  curve  is  not  shown  here  for  this  single  experiment. 


UNIVERSITY 


OF 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      17 

it  is  probable  that  a  second  determination  on  the  same  sample 
would  vary  on  account  of  differing  degrees  of  rehydration.  If 
some  liquid  were  used  which  had  no  effect  of  this  kind,  and  in 
which  the  finely  powdered  oxides  settled  readily  and  were  easily 
filtered,  this  effect  could  be  avoided  and  a  number  of  determina- 
tions made  upon  the  same  portion,  the  period  of  heating  in  each 
determination  being  simply  a  continuation  of  the  preceding  and 
the  effect  cumulative. 

A  number  of  such  liquids  were  tried,  including  bromoform, 
benzol,  xylol,  chloroform,  etc.  Chloroform  was  finally  selected, 
having  a  comparatively  low  boiling  point  and  easily  handled. 
On  account  of  the  low  boiling  point,  the  oxides  were  very  easily 
dried.  A  number  of  methods  were  tried  to  obtain  the  most  con- 
stant results.  The  co-efficient  of  expansion  of  chloroform  being 
larger  than  that  of  water  and  its  specific  gravity  greater,  it  was 
necessary  to  maintain  as  constant  temperature  conditions  as 
possible. 

One  method  used  was  to  employ  a  large  flask  filled  with  chloro- 
form at  room  temperature.  From  this  the  chloroform  was 
forced  by  air  pressure  into  the  gravity  flask,  in  order  to  avoid 
handling;  a  thermometer  was  kept  in  the  chloroform  at  all  times, 
but  the  variations  in  weight  were  too  great  for  even  as  accurate 
work  as  in  the  case  where  water  was  used,  and  this  method  was 
discarded. 

A  second  method  was  to  use  a  constant  temperature  bath,  as 
follows:  A  large,  three-liter  beaker  served  as  the  bath,  being 
well  protected  by  cloth  and  felt.  A  smaller  beaker,  of  tall  form, 
about  700  cc.  capacity,  was  suspended  in  the  center  of  the  larger 
one  by  a  wooden  cover,  provided  with  a  hole  of  proper  size.  The 
smaller  beaker  was  nearly  filled  with  chloroform  and  the  larger 
beaker  filled  with  water.  Before  each  determination,  the  gravity 
flask  was  immersed  in  the  chloroform  and  the  liquid  agitated 
until  the  temperature  was  constant.  The  flask  was  filled  and 
the  stopper  inserted  while  still  in  the  chloroform  vapor.  It  was 
found  impossible  to  obtain  concordant  weights  for  the  flask 
filled  with  chloroform  in  this  way,  and  the  method  was  aban- 
doned. 

A  third  method  was  decided  upon  and  used  throughout    the 


18      Specific  Gravities  of  Niobium  and  Tantalum  Penioxides 

remainder  of  the  work.  To  obtain  a  constant  temperature  a 
bath  of  boiling  chloroform  was  used  and  the  flask  placed  in  its 
vapor.  The  chloroform  was  boiled  in  a  Victor  Meyer  vapor 
density  tube  and  the  gravity  flask  suspended  in  a  wire  basket 
about  an  inch  and  a  half  above  the  boiling  chloroform.  A  ther- 
mometer, graduated  to  hundredths  of  a  degree  C.,  was  suspended 
in  the  tube  to  record  temperatures.  Platinum  wire  was  used 
to  insure  uniform  boiling  and  the  heat  was  supplied  by  an  electric 
hot  plate. 

No  reflux  condenser  was  needed,  as  the  vapor  was  all  con- 
densed about  three  or  four  inches  from  the  top  of  the  tube  The 
temperature  of  the  vapor  varied  about  0.6°  on  different  days 
(from  60.40°  to  61.03°),  depending  upon  the  barometric  pressure. 
This,  however,  did  not  affect  the  accuracy  of  the  weights,  since 
the  two  required  for  a  determination  were  taken  in  comparatively 
short  intervals  of  time,  and  the  barometric  change  in  that  time 
was  negligible. 

A  gravity  flask  with  a  long  and  well-fitted  stopper,  but  with- 
out a  vacuum  jacket,  was  used.  Determinations  were  made 
as  follows:  The  flask  filled  with  chloroform  was  heated  for  ten 
minutes  in  the  bath,  allowed  to  cool  ten  minutes  and  weighed, 
the  cap  being  placed  on  the  flask  as  soon  as  the  small  amount 
of  chloroform  on  the  outside  had  evaporated.  This  was  prac- 
tically accomplished  by  the  time  the  flask  had  been  removed 
from  the  tube.  The  flask  was  then  emptied  and  a  weighed 
amount  of  oxide  introduced.  It  was  partially  filled  with  chloro- 
form and  again  heated.  This  served  to  remove  any  air  that  might 
be  included  in  the  powdered  oxide.  The  flask  was  then  re- 
moved from  the  bath,  shaken  with  a  rotary  motion,  filled,  and 
the  stopper  replaced,  again  suspended  in  the  bath  and  the  heat- 
ing continued  for  ten  minutes  longer.  The  weight  was  taken 
after  allowing  to  cool  ten  minutes. 

It  is  important  that  the  flask  be  only  partially  filled  when 
suspended  in  the  bath  for  the  first  time,  for  if  completely  filled, 
vapor  invariably  forms  inside  the  flask,  causing  serious  errors. 
It  is  equally  important  that  the  lower  surface  of  the  stopper  be 
rounded  and  well  polished.  It  is  also  required  that  the  oxide 
be  dried  on  the  filter  paper  and  then  removed  before  reheating 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      19 

for  another  determination.  If  the  paper  is  incinerated  with  the 
oxide,  vapor  always  forms  in  the  flask  when  this  oxide  is  again 
employed  for  a  gravity  determination. 

The  average  of  four  weights  of  the  flask  filled  with  chloroform 
and  an  average  of  the  same  number  of  weights  with  the  flask 
filled  with  water  in  the  same  bath  was  made.  The  weight  of  the 
flask  alone  being  known,  the  ratio  of  chloroform  to  water  at  this 
temperature  (60.80°  C.)  was  found  to  be  1.432. 

The  material  for  the  following  experiments  was  prepared  in  a 
somewhat  different  manner  from  that  of  the  first  part.  A  large 
quantity  of  niobium  double  fluoride  was  treated  in  small  lots 
until  about  50  grams  of  the  pure  oxide  was  prepared.  This  was 
then  placed  in  a  large  crucible  and  heated  for  one  hour  at  a  full 
red  heat,  avoiding  thereby  the  probability  of  separate  portions 
differing  in  specific  gravity  on  account  of  slight  but  unavoidable 
differences  in  preparation. 

A  number  of  determinations  was  made  on  the  oxide  prepared 
as  just  described.  It  was  thought  at  first  that  a  weight  could 
be  determined  upon  by  a  series  of  weighings  which  would  be 
constant  for  the  flask  filled  with  chloroform.  But  it  was  found 
that  a  separate  weighing  must  be  made  for  each  determination, 
as  before.  This  was  due  to  the  difference  in  barometric  pressure 
on  different  days  and  the  same  gradual  increase  in  weight  of  the 
flask  for  a  time  and  after  a  period  of  rest,  a  return  to  nearly  the 
original  weight,  as  mentioned  in  the  case  where  water  was  used 
(page  10). 

Gravity 

Weight  Flask         Weight  Flask  Weight  Referred 

No.  and  CHC13.  and  Oxide.  Oxide.  to  CHC13. 

51 30.2674  30.9878  1.0220  3.388 

52 30.2692  30.9826  1.0127  3.383 

53 30.2683  30.9818  1.0134  3.380 

54 30.2683  30.9955  1.0330  3.375 

55 30.2674  30.9792  1.0160  3.340 

56 30.2684  30.9806  1.0176  3.340 

57 30.2670  30.9757  1.0123  3.334 

The  last  three  results  were  made  upon  a  different  lot  of  oxide  r 
prepared,  however,  as  nearly  as  possible  in  the  same  manner. 
Another  sample  of  oxide,  prepared  as  nearly  as  possible  as  before, 
gave  the  following  results: 


20      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

Gravity  Referred 

No.  Weight  Oxide.  to  CHC13. 

58 1.0138  3.238 

59 1.0192  3.248 

60 1.0151  3.227 

61 1.0400  3.224 

62 1.0337  3.236 

63 1.0349  3.244 

64 1.5238  3.234 

65 2.0475  3.224 

These  results  show  a  maximum  difference  of  0.024,  which  was 
regarded  sufficiently  accurate  for  this  work.  The  results  on  the 
three  different  samples  (Nos.  51-54,  55-57  and  58-65)  differing 
as  they  did,  showed  beyond  question  that  the  method  of  prepa- 
ration and  the  length  of  time  of  heating  the  oxide  were  ver}r 
important  factors  in  obtaining  a  constant  specific  gravity. 

This  led  to  a  series  of  determinations  on  one  sample,  heating 
a  specified  time  before  each  determination,  to  find  if  any  point 
could  be  reached  where  the  gravity  remained  practically  con- 
stant. 

For  this  purpose  a  quantity  of  the  niobium  pentoxide  was 
prepared  in  the  usual  way  in  small  quantities  and  the  entire  lot 
thoroughly  mixed  and  heated  for  one  hour  at  a  full  red  heat. 
From  this  lot  the  portions  for  the  following  experiments  were 
taken.  Each  group  represents  the  determinations  on  one 
sample  until  the  gravity  remained  practically  constant.  The 
temperature  employed  for  these  ignitions  was  a  full  red  heat. 

Weight  Time  of  Gravity  Referred 

No.  Oxide.                      Heating.  to  CHC13. 

66 1.2230  20  mins.  3.186 

67 1 .2008  20      "     more.  3. 178 

68 1.1956  25      "         "  3.166 

69 1.1822  25      "         "  3.152-> 

70 1.1829  25      "         "  3.158/A 

71 1.2339  20  mins.  3.188 

72 1.2298  20      "     more.  3.171 

73 1.2114  30      "         "  3.166 

74 1.2055  25      "         "  3'159\D 

75  ..  .  1.2026  20      "         "  3.159J  B 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      21 


Weight 

No.  Oxide. 

76 1.2361 

77 1.2415 

78 1 . 2354 

79 1.2243 

80 1.2223 

81 1.2145 

82 1.2094 

83 1.1987 

84 1 . 1851 

85  ..                    .  1.1861 


Time  of 
Heating. 

50  mins. 

20       "     more. 

20      " 

30       " 
20       " 

20  mins. 

20       "     more. 

30       " 

20       " 

20       " 


Gravity  Referred 
to  CHC13. 


3.162 
3.159 
3.161 
3.156  j 
3.160J 

3.183 

3.178 

3.159^ 

3.162 

3.159' 


C 


In  each  of  these  groups  the  gravity  gradually  diminished  until 
it  became  practically  constant. 

In  the  next  experiments  two  portions  of  about  three  grams 
each  of  K^NbOFs.H^O  were  taken  and  the  oxide  prepared  in  the 
usual  way.  Determinations  were  made  on  these  to  see  if  the 
gravity  would  reach  approximately  the  same  value  obtained 
above. 

Gravity  Referred 
to  CHC13. 
3.300 
3.190 
3.161  > 
3.159  IE 
3.159J 


Weight 

No.  Oxide. 

86 1.2855 

87 1.2658 

88 1 . 2555 

89 1.2473 

90 1.2375 

91 0.9570 

92 0.9304 

93 0.9079 

94 0.9175 

95  ..  .  0.9141 


Time  of 
Heating. 

30  mins. 

35       "     more. 

20       " 

20       " 

20       " 

20  mins. 

25       "     more. 

30       " 

30       " 

20       " 


3.346 
3.242 
3.174 
3.161 
3.158 


The  final  values  obtained  in  the  last  two  groups  agree  fairly 
well  with  those  obtained  above  and  were  included  in  the  general 
average.  The  results  marked  A,  B,  C,  D,  E  and  F  were  assumed 
to  be  constant  and  the  average  gave  3.159. 

Later  in  the  work  the  gravity  of  niobium  was  re-determined 
to  see  if  the  results  obtained  above  could  be  duplicated  under  the 
same  conditions.  An  average  of  three  closely-agreeing  values 
gave  3.161. 


22      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

Tantalum  Pentoxide 

The  method  employed  for  the  preparation  of  the  tantalum 
pentoxide  was  the  same  as  that  described  for  the  niobium  pent- 
oxide.  Each  of  the  groups  shown  below  represents  determina- 
tions on  a  separate  portion  of  oxide  taken  from  one  stock  supply. 

Weight  Time  of  Gravity  Referred 

No.  Oxide.  Heating.  to  CHC13. 

96 1.2236  40  mins.  6.191 

97 1.1985  20       "     more.  6.127 

98 1.1900  20      "         "  6.140 

99 1.1852  20      "         "  6.0971 

100 1.1775  20      "         "  6.084JA 

101 1.2010  40  mins.  6.062 

102 1.1943  20       "     more.  6.093 

103 1.1895  20       "         "  6.205 

104 1.2841  20  "     "  6.0851 

105 1.1760  20      "         "  6.090/B 

106 1.2117  20  mins.  6.098 

107 1 .2001  20       "     more.  6.097 

108 1.1828  20      "         "  6.079 

109 1.1824  20      "         "  6.0671 

110 1.1680  20      "         "  6.055/C 

111 1.2158  40  mins.  6.018 

112 1.2004  20"         more.  6.096 

113 1.1872  20      "         "  6.057 

114 1.1789  20      "         "  6.077 

115 1.2201  40  mins.  6.061] 

116 1.2019  20      "     more.  6.070 

117 1.1855  20      "         "  6.061  [  E 

118 1.1784  20      "         "  6.074  j 

119 1.1766  20      "         "  6.087  | 

120 1.1644  20       "         "  6.064J 

The  agreement  is  not  as  satisfactory  as  in  the  case  of  the 
niobium,  but  those  marked  A,  B,  C,  D  and  E  are  taken  as  con- 
stant and  averaged.  This  gives  6.073  as  the  value  of  tantalum 
pentoxide  under  these  conditions.  This  value,  with  that  of  nio- 
bium pentoxide,  3.159,  was  used  to  plot  a  curve.  (Curve  I.) 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      23 


Mixtures  of  the  two  pure  oxides  were  now  made,  fused  with 
potassium  bisulphate,  and  the  oxides  obtained  in  the  usual 
manner.  Determinations  were  made  on  these  mixtures  in  the 
same  way  as  those  above  until  the  specific  gravity  became  more 
or  less  constant. 


No. 

Weight 
Ta205. 

Weight 
Nb205. 

Per 

Cent. 

Per 
Cent. 
Nb205 

Weight 
Oxide. 

Time  of 
Heating. 

Gravity 
Referred 
to  CHCls 

Nb205 
from 
Curve. 

Error. 

121 

0.1224 

1.0826 

10.15 

89.85 

1  .  2044 

30  mins. 

3.575 

1.1892 

30       "     more. 

3.565 

1.1732 

30       " 

3.517 

1.1246 

40       " 

3.481 

89.00% 

0.85% 

122 

0.2417 

0.9617 

20.09 

79.91 

1.0515 
1.0289 

40  mins. 
20       "     more. 

3.8361 

3.  844  I 

76.60% 

3.31% 

123 

0.3614 

0.8416 

30.05 

69.95 

1  .  1952 

30  mins. 

3.962 

72.50% 

2.55% 

124 

0.4813 

0.7211 

40.03 

59.9? 

1.1518 
1.1293 

30  mins. 
30      "     more. 

4.209) 
4.201J 

64.20% 

4.23% 

125 

0.1218 

1.0808 

10.12 

89.88 

1.1348 

20  mins. 

3.431 

1  .  1054 

30      "     more. 

3.367 

92.80% 

2.92% 

126 

0.1219 

1.0813 

10.14 

89.86 

1.2032 

80  mins. 

3.343 

1  .  1845 

20      "     more. 

3.369 

1.1757 

40      " 

3.352 

93.40% 

3.54% 

127 

0.4059 

0.7962 

33.77 

66.23 

1.2021 

80  mins. 

3.794 

1.1868 

20      "     more. 

3.807 

77.60% 

11.37% 

(121)  Before  these  determinations  were  made,  the  mixture  of 
oxides  was  heated  for  one  hour  at  a  full  red  heat. 

(122)  This  mixture  was  prepared  as  in  (121)  with  the  excep- 
tion that  after  heating  for  one  and  a  half  hours  the  oxides  were 
ground  and  boiled  with  water,  to  remove  any  possible  soluble 
impurity.     On  filtering,  the  powder  was  too  fine  and  ran  through 
the  filter  to  some  extent.     It  was  washed  with  alcohol,  dried 
and  taken  from  the  paper.     Heat  was  applied  for  twenty    min- 


CURVE  I 
One  Division  =  0.02  Specific  Gravity  or  !.0 


per  cent. 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      25 

utes,  the  oxides  cooled  and  placed  in  a  desiccator  for  four  hours, 
heated  again  for  twenty  minutes,  and  the  first  determination 
made. 

(123)  This   mixture  was  treated   as   before   until  the   oxides 
were  again  obtained.     These  were  then  heated  for  one  hour  at 
a  full  red  heat,  cooled  in  a  desiccator,  again  heated  for  twenty 
minutes  and  the  determination  made. 

(124)  In  this   case,   after  obtaining  the  hydroxides  the  first 
time,  they  were  dissolved  in  hydrofluoric  acid,  filtered,  the  solu- 
tion taken  down  to  fumes  with  sulphuric  acid  and  rehydrolyzed. 
The  oxides  were  dried,  heated  one  and  a  half  hours,  pulverized, 
heated  again  for  thirty  minutes  and  the  gravity  taken. 

(125)  After  the  hydroxides  had  been  obtained  by  fusion  with 
potassium  bisulphate  and   hydrolyzing  they   were  dissolved   in 
hydrofluoric  acid,  filtered,  taken  down  to  fumes  with  sulphuric 
acid,  again  hydrolyzed,  washed  and  dried  as  usual.     Heat  was 
applied  for  one  and  a  half  hours,  the  oxides  powdered  and  heated 
again  for  20  minutes  and  the  first  determination  made. 

(126)  In  this  case  the  oxides  were  merely  mixed  and  not  fused 
with    potassium    bisulphate.     This    should    have    given    results 
according  to  the  curve,  being  a  simple  mixture.     Before  the  first 
determination  they  were  heated  for  one  hour  and  twenty  min- 
utes. 

(127)  This  experiment  was  of  somewhat  the  same  character 
as  126,  but  in  this  case  the  oxides  were  heated  separately  for  one 
hour  and  twenty  minutes,  weighed,  mixed,  weighed  again  and 
the   specific   gravity  taken.     In   the   second   determination  the 
two.  mixed,  were  heated  for  twenty  minutes  and  the  specific  grav- 
ity taken. 

These  results  are  unreliable  from  a  quantitative  point  of  view 
and  could  not  be  depended  upon  for  the  estimation  of  Nb20s 
and  Ta2C>5  in  mixtures. 

In  order  to  determine  if  any  change  in  weight  took  place  on 
ignition  of  the  oxides,  quantities  of  each  were  taken,  ignited  one 
hour  and  weighed.  They  were  then  ignited  one  hour  longer 
(Chaddock  burner)  and  the  loss  in  weight  determined.  1.0026 
grams  Nb2O5  lost  0.0028  gram  and  1.0011  grams  Ta2O5lost  0.0012 
gram.  The  crucible  itself  showed  no  loss  in  weight. 


26      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

Similarly,  4.0357  grams  Ta20s;  which  had  been  ignited  with 
the  blast  lamp  for  fifteen  minutes,  lost  0.0010  gram  on  blasting 
for  twenty-five  minutes  longer,  and  5.0083  grams  Nb20s  lost 
0.0045  gram  on  blasting  for  twenty-five  minutes. 


III 

It  was  next  decided  to  try  the  effect  of  the  blast  lamp  on  the 
gravity  of  the  pure  oxides,  in  order  to  establish  a  new  basis  for 
a  curve  to  use  with  a  series  of  mixtures,  hoping  by  this  means 
to  obtain  constant  results. 

Determinations  were  made  on  two  portions  of  niobium  pent- 
oxide,  blasting  each  time,  until  the  gravity  became  practically 
constant. 

Weight  Time  of  Gravity  Referred 

No.  Oxide.  Heating.  to  CHC13. 

128  ............    1.4951  20  mins.  3.170 

129  ............    1.4752  20       "     more.  3.230 

130  ............    1.4646  20       "         "  3.227 

131  ............    1.4545  20       "         "  3.262] 

132  ............    1.4479  20       "         "  3.2621 

133...  .........    1.4396  20      "         "  3.268  [ 

134.  .   1.4357    '  20      "         "  3.283'' 


135 1.4270  20  3.262 

136 1.4273  20      "         "  3.280J 

137 1.4945  20  mins.  3.228} 

138 1 .4848  20      "     more.  3.255  >  B 

139 1.4715       20   "    "  3. 255-* 

140 1.4629       20   "    "         3.263 

The  average  of  those  marked  A  and  B  is  3.265. 
Determinations  were  made  in  the  same  manner  on  tantalum 
pentoxide  and  gave  the  following  results: 

Weight  Time  of  Gravity  Referred 

No.  Oxide.  Heating.  to  CHC1 . 

141 1 .4528  20  mins.  6.2061 

142 1 .4309  20      "     more.  6. 189 

143 1.4211  20       "         "  6.212 

144 1.4122  20       "         "  6.226  j-A 

145 1.4064  20      "         "  6.236 

146 1.3935  20      "         "  6.204 

147 1.3909  20      "         "  6.195j 


Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides       27 


No. 
148 

Weight 
Oxide. 
1  4971 

149  

1  .  4735 

150 

1  4695 

151  

1  .  4622 

152  .  .  . 

...  1  4562 

153 

1  4504 

154  
155  .  . 

1.4471 
.  1.4404 

Time  of 
Heating. 


20  mins. 

20  " 

20  " 

20  " 

20  " 

20  " 

20  "' 

20  " 


Gravity  Referred 

tO*CHCl3. 

6.183 
6.155 
6.166 
6.1961 
6.194  I 
6.193  I-B 
6.218  j 
6.203J 


Those  marked  A  and  B  were  averaged  and  gave  6.201.  The 
values  just  obtained  for  tantalum  and  niobium  oxides  were  used 
in  plotting  Curve  II. 

A  series  of  mixtures  was  now  made,  nine  in  all,  from  10  per 
cent,  to  90  per  cent,  tantalum.  These  were  heated  with  the 
full  heat  of  the  Chaddock  burner  until  a  practically  constant 
gravity  was  obtained,  then  to  the  same  mixture  the  blast  was 
applied  for  definite  periods  until  another  constant  value  was 
reached.  The  first  part  of  each  group  represents  the  determina- 
tions with  the  lower  heat  and  the  second  part  the  results  obtained 
by  blasting. 


No. 

Weight. 

Per  Cent. 

Weight 
Oxide. 

Time  of 
Heating. 

Gravity 
Referred 
to  CHC13 

Aver- 
age. 

Ta205 

Nb205 

Ta205 

Nb205 

156 

0.1228 

1.0812 

10.20 

89.80 

1.1637 

90  mins. 

3.500 

.1083 

30       "     more. 

3.467 

.0942 

40       " 

3.304 

.0825 

110       " 

3.240 

.0677 

20       " 

3.220 

.0725 

30       " 

3.225 

Blast 

1.0715 

15      " 

3.356 

157 

1.0699 
1.0562 

30      " 
15      " 

3.3151 

3.317  J 

3.316 

0.2415 

1.0812 

20.06 

79.94 

1.1497 

90  mins. 

3.890 

1.1286 

60      "     more. 

3.758 

1.1192 

20      " 

3.699 

1  .  1029 

60      "         " 

3.523 

1.0935 

30      " 

3.516 

28      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 


Weight. 

Per  Cent. 

Gravity 

No. 

Weight 

Time  of 

Referred 

Aver- 

Ta205 

Nb205 

Ta205 

Nb205 

Oxide. 

Heating. 

to  CHC13 

age. 

1.0995 

60       " 

3.488 

1.0858 

30       " 

3.664 

1.0726 

40       " 

3.448 

1.0410 

20       " 

3.418 

0.0454 

20       "         " 

3.453 

1.0451 

30      "         " 

3.432 

1.0487 

30      " 

3.432 

Blast 

1.0480 

15      " 

3.414 

1.0487 

15      " 

3.438 

1.0459 

15      " 

3.464 

0.0447 

15       " 

3.488 

1.0377 

15       " 

3.497 

1.0367 
1.0257 

15      " 
15       " 

3.4811 

3.487  1 

3.  434 

158 

0.3627 

0.8420 

30.10 

69.90 

1.1540 

120  mins. 

4.157 

1.1396 

40       "     more. 

4.200 

1.1330 

50      " 

4.177 

1.1231 

20       " 

4.182 

1.1217 

20       " 

4.154 

1.1117 

20      " 

4.184 

1  .  1028 

20      " 

4.186 

Blast 

1.0931 

15       " 

3.378 

1.0849 

15      " 

3.648 

1.0747 

15       " 

3.656 

1.0696 
1.0682 

15       " 

15       " 

3.6931 
3.680/ 

3.686 

159 

0.4816 

0.7209    40.05 

59.95 

1.1513 

90  mins. 

4.440 

1.1303 

20       "     more. 

4.422 

1  .  1231 

60       " 

4.420 

Blast 

1.1103 

15      " 

4.017 

1.0961 

15      " 

3.904^ 

1.0852 

15      " 

3.919  I 

3.908 

1.0808 

15      " 

3.901  J 

Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides      29 


Weight. 

Per  Cent. 

1 

Gravity 

No. 

Weight 

Time  of 

Relerred 

Ta205 

Nb2Os 

T2aOs 

Nb205 

Oxide. 

Heating. 

to  CHCl.s 

age. 

160 

0.6016 

0.6015 

50.02 

49.98 

1  .  1404 

120  mins. 

4.583 

1.1182 

30       "     more. 

4.642 

1.1017 

30       " 

4.642 

1.0910 

20       " 

4.644 

Blast 

1.0884 

15       " 

4.366 

1.0875 

15       " 

4.308 

1.0881 

15       " 

4  .  282 

1.0835 

15       " 

4  .  148 

1.0781 

15       " 

4.169 

1.0792 

15       " 

4.163 

1.0780 

15       " 

4.142 

1.0736 

15       " 

4.080 

1.0721 
1.0715 

15       " 
15       " 

4.0741 
4.074  / 

4.074 

161 

0.7210 

0.4810 

59.98 

40.02 

1.1592 
1.1414 

120  mins. 
20       "     more. 

4.786 

4.857 

1.1293 

20       " 

4.878 

1.1129 

20       " 

4.868 

Blast 

1.1136 

15      " 

4.848 

1.1146 

15       " 

4.903 

1  .  1090 

20       " 

4.926^, 

1  .  1006 
1.0988 

15      " 

15       " 

4.926  i 
4.916  f 

4.925 

1.0947 

15       " 

4.93lJ 

162 

0.8411 

0.3616 

69.94 

30.06 

1.1323 

90  mins. 

5.123 

1.1163 

20       "     more. 

5.189 

1  .  1055 

20       " 

5.202 

1.0992 

30      " 

5.194 

1.0895 

60      " 

5.271 

1.0821 

30      " 

5.253 

1.0781 

20      " 

5.266 

Blast 

1.0704 

15      " 

5.221-j 

1.0697 

15       " 

5.223[ 

5.227 

1.0637 

15       " 

5.237^ 

30      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 


No. 
163 

Weight. 

Per  Cent. 

Weight 
Oxide. 

Time  of 
Heating. 

Gravity 
Referred 
to  CHC13 

Aver- 
'  age. 

Ta205 

Nb205 

Ta2Os 

Nb2Os 

0.9612 

0.2410 

79.95 

20.05 

1.1102 

90  mins. 

5.178 

1.0883 

20      "     more. 

5.301 

1.0814 

20       " 

5.337 

1.0796 

50      " 

5.363 

1.0681 

80      " 

5.460 

1.0588 

40       " 

5.443 

1.0573 

30      " 

5.469 

Blast 

1.0484 

15       " 

5.454 

1.0452 

15      " 

5.486 

1.0416 

15      " 

5.522 

1.0354 

30      " 

5.475 

1.0342 

15      " 

5.530 

5.530 

164 

1.0823 

0.1229 

89.80 

10.20 

1.1360 

120  mins. 

5.601 

1.1126 

30      "     more. 

5.816 

1.1015 

20       "         " 

5.773 

1.0967 

30      " 

5.808 

1.0857 

30      " 

5.774 

Blast 

1.0803 

15      " 

5.827 

1.0819 
1.0788 
1.0709 

15      " 
15      " 
15       " 

5.845} 
5.838h 
5.845  J 

5.843 

Although  the  values  obtained  on  these  mixtures  do  not  fall 
on  the  curve  obtained  from  the  pure  oxides,  nevertheless,  they 
are  quite  regular,  the  greatest  variation  among  themselves  being 
about  one  per  cent.  It  is  interesting  to  note  the  sudden  break 
in  the  curve  between  the  40  and  50  per  cent,  mixtures.  Whether 
or  not  this  break  is  due  to  the  formation  of  a  compound  of  the 
two  oxides  the  author  was  unable  to  determine. 

In  view  of  the  fact  that  the  curve  obtained  on  these  mixed 
oxides  was  so  regular,  it  was  hoped  that  satisfactory  results 
might  be  obtained  on  the  analysis  of  a  sample  of  columbite. 
The  mineral  used  was  the  same  "Columbite  A"  analyzed  volu- 
metrically  by  Metzger  and  Taylor,1  which  gave  an  average  value 


1  To  be  published  soon. 


3.465 


3.265 


10%      20%      30%      40%      50%      60%      70%      80%      90%      100% 

CURVE  II 
One  Division  =  0.02  Specific  Gravity  or  1.0  per  cent. 


32      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 


of  54.21  per  cent,  niobium  pentoxide  and  22.75  per  cent,  tan- 
talum pentoxide,  which  means  that  the  mixed  oxides  would  be 
composed  of  70.43  per  cent,  niobium  pentoxide  and  29.57  per 
cent,  tantalum  pentoxide. 

Three  different  portions  were  treated,  as  follows:  The  ore  was 
fused  with  potassium  bisulphate  and  the  melt  boiled  with  about 
one  liter  of  water.  The  impure  hydroxides  so  obtained  were 
filtered,  washed  with  boiling  water  until  the  filtrate  gave  only 
a  faint  test  for  sulphuric  acid,  treated  on  the  filter  with  yellow 
ammonium  sulphide,  washed  again  and  treated  with  hot  dilute 
sulphuric  acid.  The  washed  hydroxides  were  dissolved  through 
the  filter  paper  with  hydrofluoric  acid,  the  solution  taken  down 
to  furnes  with  sulphuric  acid,  rehydrolyzed,  boiled  with  water 
and  washed  by  decantation  twice,  the  last  wash  water  being 
made  alkaline  with  ammonium  hydroxide.  The  hydroxides 
were  then  filtered,  dried,  blasted  for  definite  periods  and  the 
gravity  taken. 


Amount 

Weight 

Per  Cent. 

Gravity 

No. 

Ore 

of 

oi 

Weight 

Time  of 

Referred 

Aver- 

Taken. 

Oxides. 

Oxides. 

Oxides. 

Heating. 

to  CHCls- 

age. 

165 

2.0023 

1.5458 

77  .  25 

1  .  5266 

30  mins. 

3.487 

1.5011 

20       "     more. 

3.514 

.4929 

20       " 

3.560 

.4857 

20       " 

3.578    • 

.4764 

20       " 

3.587 

.4692 

40       " 

3.592 

.4656 

20       " 

3.610] 

1.4620 
1.4586 
1.4568 
1.4502 

20       " 
25       " 
20       " 
20       " 

3.618 
3.616  }• 
3.600  I 
3.618J 

3.612 

1G6 

2.0019 

1.5446 

77.15 

1.5279 

20  mins. 

3.479 

1.5159 

40       "     more. 

3.519 

1.5052 

20       " 

3.553 

1.5049 

20       " 

3.574 

1.4981 

20      " 

3.599 

1.4927 

20       " 

3.599 

1.4938 
1.4910 

1.4872 

25       " 
20       " 

20       " 

3.617} 
3.612  [ 

3.620^ 

3.616 

Specific  Graviteis  of  Niobium  and  Tantalum  Pentoxides      33 


Amount 

Weight 

Per  Cent. 

Gravity 

No. 

Ore 

of 

of 

Weight 

Time  of 

Referred 

Aver- 

Taken. 

Oxides. 

Oxides. 

Oxides. 

Heating. 

to  CHC1. 

age. 

167 

2.0000 

1.5382 

76.91 

1.5271 

20  mins. 

3.282 

1.5081 

20       "     more. 

3.462 

1.4985 

20       " 

3.543 

1.4908 

75       "         " 

3.572) 

1.4918 

20       " 

3.580  f 

3.577 

1.4840 

40       " 

3.578' 

(165)  According  to  the  curve,  the  value  3.612  gives  74.4  per 
cent.  Nb2O5,  and   calculating  from  this,  the  ore  contains  57.43 
per  cent.  Nb2O5,  an  error  of  3.22  per  cent. 

(166)  This  value,  3.616,  is  very  close  to  that  of  165  and  the 
per  cent,  of  Nb20s  cannot  be  read  closer  than  74.4  per  cent,  on 
the  curve.     This  gives  57.47  per  cent.  N^Os  in  the  ore.  an  error 
of  3.24  per  cent. 

(167)  The  value  3.577  gives  76.4  per  cent,  as  the  amount  of 
Nb2Os  in  the  mixture.     This  is  equal  to  58.75  per  cent.  Nb2Os  in 
the  ore,  an  error  of  4.54  per  cent. 


CONCLUSIONS. 

The  mixtures  of  oxides,  as  prepared  by  fusion  with  potassium 
bisulphate,  hydrolysis,  etc.,  do  not  follow  the  straight  line  of  the 
curve. 

The  specific  gravity  of  the  oxides  varies  slightly  with  the  method 
of  preparation  and  greatly  with  the  length  of  time  and  intensity 
of  the  heating. 

As  a  method  for  the  determination  of  the  percentages  of 
niobium  and  tantalum  in  a  mixture  of  the  two  oxides,  it  can 
only  be  relied  upon  to  an  accuracy  of  about  five  per  cent. 

In  general,  the  specific  gravity  of  niobium  pentoxide  decreases 
with  increase  in  temperature  and  length  of  time  of  heating,  while 
that  of  tantalum  pentoxide  increases  under  the  same  conditions. 

The  average  values  of  the  specific  gravity  of  niobium  and  tan- 
talum pentoxides  under  the  different  conditions  tried  are: 


34      Specific  Gravities  of  Niobium  and  Tantalum  Pentoxides 

Referred  to  Referred  to 

NIOBIUM  PENTOXIDE.                                water.  chloroform. 

At  a  low  red  heat 4 . 949  

At  a  bright  red  heat 4 . 828  3 . 159 

At  temperature  of  blast 3 . 265 

TANTALUM  PENTOXIDE. 

At  a  low  red  heat 7 . 872  

At  a  bright  red  heat 8 . 328  6 . 073 

At  temperature  of  blast 0.201 


THE 

UNIVERSITY 


THIS  •f-XSSft 


jjf:  V^ 


20m-- 


